Orson Welles once told an interviewer that he considered the greatest screen actor of all time to be Jimmy Cagney. The reason he gave for this was that Cagney always played at the top of his range but was never fake or over-the-top.
The effect of this full-on style of acting was magnetic. When somebody is pouring their all into what they’re doing, you can’t help but watch. Most actors can do this when the script requires. Cagney could do it all the time. Love scene, death scene, action scene.
It doesn’t matter how big you go if you can make it feel real. And because the audience believes the actor cares, they care.
When it comes to writing fiction you can use a similar approach to keep the reader engaged with what’s happening in the story.